Conventional AC plasma display technology includes display panels comprising two glass plates having orthogonally positioned conductor arrays thereon encapsulated in a gas envelope, the intersections of said conductor arrays forming gas cells. The conductor arrays are overcoated with a dielectric and insulated from the gas and thus capacitively coupled to the gas in the panel. When signals exceeding the ionization potential of a pair of conductors occur during a write operation, a discharge takes place and a wall charge potential is formed on the cell walls. This potential combines with a lower level sustain signal to continuously discharge the cell at a relatively high frequency (40 KC) to maintain the discharge, while erase takes place by neutralizing the wall charge and thereby removing the wall charge potential.
The operation of an AC plasma display panel thus requires the application of sequences of three control signals, i.e., sustain, write, and erase. These signals are applied to drivers which control the energization state of the illuminable cells in the plasma panel display and are sequenced so as to provide the sustain, write, and erase operations required in the plasma panel display. The sustain operation has two separate applications. The first application as described above is to maintain the information on the plasma panel display in its then present state. The second application is to normalize a write or an erase operation by a sustain sequence. If a sustain sequence is not properly applied before and after write and erase operations, then the write or erase operation will not be successfully completed. In the preferred embodiment herein described, a plurality of three sustain sequences are required after a write or an erase operation for normalization of the cells.
A plasma panel display may be controlled by a data processing system or controller which serves two purposes in relation to the display. First, it sends data signals which are representative of the information that is to be displayed. Second, it sends the control commands, such as write or erase, which cause the information to be displayed by or erased from the plasma panel display. These control commands are received by the plasma panel through appropriate control circuitry and are operated upon so as to effect the appropriate control operations of write, sustain, and erase.
One method of accomplishing such plasma panel control is disclosed in U.S. Pat. No. 3,851,211 where individual control sequences of the sustain, write and erase signals are stored within a ROS. Logic circuitry within the panel assembly but external to the ROS, receives the control information from a data processing system or controller. The logic circuitry then selectively activates the appropriate control sequences of sustain, write, and erase within the ROS so as to effect control of the plasma panel display.
As the cost of storage continues to decline, it would be desirable to provide control of the individual operations of sustain, write and erase within a storage device located in the plasma panel assembly. By so doing, the external logic circuitry required in the prior art is simplified.
When hardwired logic is used to implement the controls, the transition from one sequence to another, for instance, from sustain to write, can be done in a manner whereby all appropriate control lines are changed without interruption. As described herein, the term "interruption" refers to the accuracy and timing of the appropriate control signals to the designated lines to effect the above operations. However, it is not obvious how this effect could be accomplished in a Read Only Storage (ROS) device. This is important in a plasma display because a momentary interruption of the sustain waveform, for instance, can be detrimental to the sustain margin.
When a ROS is used to implement the control, this interruption of the control sequence could occur during switching between sections of the ROS. This problem is solved in the instant invention by addition to the sequence which bridge the gaps between sequences so that no interruption occurs. The simplification of the logic circuitry can also bring with it an increase in reliability as well as a decrease in cost.
Accordingly, it is an object of this invention to provide improved ROS control of a gas panel display.
It is another object of this invention to provide a gas panel display wherein no signal discontinuity results when switching between control operations.
It is still another object of this invention to simplify the logic circuitry heretofore required to provide the control operations of write, erase, and sustain in a plasma panel display.
It is a further object of this invention to provide a plasma panel display wherein a ROS contains a sustain operation recycling sequence which automatically checks for new inputs of erase and write control commands.